1. Field of the Invention
The present invention relates in general to the field of information handling system power subsystems, and more particularly to a system and method for powering an information handling system in multiple power states.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Portable information handling systems have gained widespread acceptance among consumers as a replacement for desktop systems. Portable information handling systems integrate into a common housing a display, such as an LCD, power source, such as a battery, and I/O devices, such as a keyboard, mouse and wireless network interface card. Integration of these devices allows a portable information handling system to operate free from physical assets, such as peripheral display devices and external AC power sources. One difficulty that accompanies portable information handling system use is that the internal battery power source has a limited charge so that continuous operation of the system requires periodic recharge of the battery with an external AC-to-DC adapter. In an attempt to reduce power consumption, portable information handling systems typically employ a variety of low power states that reduce power consumption. Four common power states used by information handling systems are an on state (S0) with full power applied to all components, a standby or suspend state (S3) with power applied to RAM to maintain an active operating system for rapid power-up to the on state, a hibernate state (S4) where the active operating system and open data files stored on a hard disk drive for essentially zero power consumption and allows for a quick power-up to an on state, and an off state (S5) with no power applied. In order to save power in the standby and hibernate states, power supply rails are typically turned off in those power states to at least some components. For example, the chipset receives different amounts of power based on the power state of the information handling system.
FIG. 1 depicts an example of a conventional voltage regulator that supports reduced power states in supplying power to a chipset. A “run” power rail is active along with a “suspend” power rail when the information handling system is in an S0 “on” power state. A MOSFET load switch PQ5 prevents load current passing to components on the “run” power rail when the information handling system is in a reduced power state while load current continues to a “suspend” or “reduced power state” power rail. Typically, each power rail is built in one of plural planes of a printed circuit board, such as a motherboard. Newer generation portable CPU chipset current requirements have increased to as much as 25 Amps on some “run” rails while voltage tolerances have tightened from +/−5% to +/−2%. Therefore, for example, a 1.1 Volt rail only allows +/−22 mVolts of variation over a load range of 25 Amps as compared with previous generation variations of +/−55 mVolts. The combination of higher output and tighter tolerances has made the use of a MOSFET switch PQ5 as depicted in FIG. 1 impractical since even a high quality 2.5 mOhm MOSFET will drop 63 mVolts over a 25 Amp load range. In addition, such a MOSFET dissipates greater than 1.5 Watts of power, which increases power consumption and MOSFET thermal concerns. To avoid the use of MOSFET load switches, industry has shifted to the use of two independent switching voltage regulators as depicted in FIG. 2. A single phase voltage regulator supports a suspend reduced power state by providing power to a suspend rail while an independent two phase voltage regulator provides power to a run power rail. The 25 Amp run requirement requires the use of a two phase voltage regulator so that adequate power and load regulation are available and so that an acceptable regulator efficiency may be achieved in order to meet thermal design requirements.